1. Field of the Invention
The present invention relates to a method for modification of glass-based microchannels. It can be applied to various electrophoresis separation devices without occurrence of electro-osmosis flow effect during the material detection such as DNA, protein, anions, cations and the like.
2. Description of the Related Art
The capillary electrophoresis has been widely applied in all kinds of biochemical analysis domain for having advantages such as short separation time, less sample injection volume, high sensitivity, and convenient instrument operation. Recently, the capillary electrophoresis is further widely used in biological samples, such as protein and DNA, or chemistry-based analysis research. In 1981, Jorgenson et al. [1] used the capillary having inner diameter of 75 μm to separate the amino acid and detect fluorescence signals. This method became the basic structure of current capillary electrophoresis analysis technique. Because this method provided the advantages not found in the traditional system, it was widely utilized and developed. In recent years, following the development of micro-electro-mechanical-system (MEMS) technique, there presents various micro-fluid biomedical detection chips produced by the MEMS process. In 1992, Harrison et al. [2] employed the MEMS techniques to fabricate planar microchannels in glass for conducting the electrophoresis on capillary chip, which was associated with the optical detection system to successfully separate the samples on the glass micro-fluidic chip. Not only could this technique greatly reduce the separation time, but it also reduces the sample usage and the analysis cost.
However, the main material for the substrate of the conventional glass capillary or producing planar microchannels is the fused silica, wherein the Si—OH on the surface is easily dissociated to form the Si—O− with negative charges. Thus, when the capillary is full of the buffer solution, it will form the electro-double-layer (EDL), wherein the first layer is a stern layer formed by attaching with positive material in the solution attracted by the negative Si—O− on the capillary wall; and, the second charged layer is formed by superfluous positive material attracted simultaneously at farther location on the capillary wall, and the charge density is decreased in an exponential trend with the increased distance from the capillary wall to form the diffusion layer. Due to the existence of the EDL, it will induce the Zeta potential between the capillary wall and the operation solution. Under the effect of the electrical field, the solution in the capillary will flow entirely, so as to generate the bulk motion of electro-osmosis flow (EOF), which is characterized in that the fluid velocity in the microchannel is uniformly distributed, but not the parabolic distribution for the conventional pressure-driven pipe flow. The mobility of the electro-osmosis flow for the solution in a uniform electric field is given as the formula below:
            μ      eo        =          ɛζ      η        ,wherein,    μeo: mobility of electro-osmosis flow in the solution    ∈: dielectric constant of the solution    ζ: interface potential (Zeta potential)    η: viscosity of the solution.
On the other hand, in the capillary electrophoresis, because the charged particles have their own electrical electrophoresis mobility μep, and the solution itself also has the electro-osmosis flow mobility μeo, the actually observed overall mobility μap is the sum of both values.μap=μeo+μep 
The positive ions are attracted by the negative electrodes, and also with the electro-osmosis flow speed to cause the materials with positive charges to move faster (μe0 and μep have the same direction), and the materials with negative charges are repulsive with the negative electrodes (cathodes) and moving in a lower speed (μeo and μep have the opposite directions). The moving speed of neutral ions equals to the electro-osmosis flow. Thus, if it is the electro-osmosis flow in the system that channels the flow of the separating material, the separation efficiency would be undesirable, or even not able to separate samples. Because the μeo and μep move in opposite directions, the material led by the electrophoresis will be brought back to the original place by the electro-osmosis flow. It can be noted that to restrain the occurrence of electro-osmosis flow becomes the key point for achieving higher or lower separation efficiency in many applications.
The method for insulating the glass surface from the operational solution by glass surface modification had been disclosed by Hjertén [3] in 1967, which used the chemical treatment to generate the covalent bonding for the —OH functional group on glass surface with silane, and cover the glass substrate with the bonded organic molecules. This method had been widely utilized. Yet in 1985, Hjertén disclosed a method of using linear polyacrylamide for the modification on the inner wall of glass capillary [4]. After this technique had been applied in the protein separation, numerous researches were conducted by using the same method for the surface modification of glass capillary for proteins, DNA or polypeptides researches. Furthermore, all kinds of different modification methods have been continuously disclosed, such as using Si—OH group on the glass surface for silanization being one of the major methods for modification [5-7]. Moreover, Schomburg et al. [8] used a series of polarized organic molecules having —NH2 group to form the covalent bonded hydrophilic molecular film on the glass surface for reducing the electro-osmosis effect on the glass surface. Furthermore, another major system uses the polyvinyl alcohol (PVA) organic molecule for forming covalent bonds with Si—O—Si chemical bonds in the glass to isolate from the glass substrate [9-10]; or, using esterization [11], or thionyl chloride and magnesium bromide to react with the glass surface [12]; or, using polyacrylamide [13], or poly(glycidyl mechacrylate) (PGMA) to form the covalent bonds with the Si—OH group on the glass surface [14] to achieve the modification. A similar method disclosed by Lwinweber in 2001 used poly(2-hydroxyethyl methacrylate) (PHEMA) organic polymer [15] to conduct the modification on capillary wall and verify the performance. Lately, U.S. Pat. No. 6,375,818 B1 disclosed using poly(vinylpyrrolidone) organic polymer for the modification of capillary [16].
The conventional glass modification methods all used organic compounds to react with the functional groups on glass surface for chemical reactions. Although these methods had been verified, there are still lots of problems needed to be solved. For example, the above-mentioned methods all need long-time chemical reactions, because the processing steps are processed one by one, thus rendering these methods unable to mass production. Therefore, tremendous amount of time would be wasted, a result that is not economically efficient. Furthermore, most of the glass surfaces have to keep moist after modification; otherwise the processed layer will be ineffective due to drying. This feature makes the capillary hard to be preserved after processing, or cost has to be spent for preservation, so as to limit the availability of commercialization. Moreover, because these methods use the Si—OH groups on the glass surface for chemical bonding, the methods are available for processing the pure silica glass, such as crystal or fused silica, but problems would be caused while processing sodium glass containing complex components. Because the sodium glass contains Na2O (13.7%), CaO (8.8%) and MgO (4.0%), components that are difficult to conduct chemical reaction with the added organic molecules. Thus, using these methods for modification might cause undesirable processing efficiency.